Stability of Adult-plant Resistance to Septoria tritici blotch in 24 European Winter Wheat Varieties Across Nine Field Environments

Septoria tritici blotch (STB) is one of the most important leaf diseases in wheat worldwide. Objectives of this study were (i) to compare inoculation and natural infection; (ii) to evaluate the level of adult-plant resistance to STB using four isolates; and (iii) to analyse environmental stability of 24 winter wheat (Triticum aestivum L.) varieties in inoculated vs. non-inoculated field trials across 3 years including nine environments (location x year combinations). Field trials were sown in split-plot design inoculated with four aggressive isolates of S. tritici plus one non-inoculated variant as main factor and 24 wheat varieties as subfactor. Septoria tritici blotch severity was visually scored as percentage flag leaves covered with lesions bearing pycnidia. Overall STB rating ranged from 8% (Solitar) to 63% (Rubens) flag leaf area affected, resulting in significant (P < 0.01) genotypic variance. Variance of genotype x environment interaction amounted to approximately 50% of the genotypic variance. Genotype x isolate interaction variance was significant too (P < 0.01) but of minor importance. Therefore, environmental stability of varieties should be a major breeding goal. The varieties Solitar, History and Florett were most resistant and stable as revealed by a regression approach, and the susceptible varieties were generally unstable. Hence, STB resistance and stability are correlated (P < 0.01), but there were some exceptions (Tuareg, Ambition). Promising candidates for an environmentally stable, effective adult-plant resistance have been identified.